Abstract
Spin dependent transport of charges is critical to the functionality of many magneto-electronic devices. Since half metals have electrons of only one spin state present at the Fermi energy, they are ideal candidates to be used as spin injectors. Fe3Si is a ferromagnet with a Tc of 840K, and can be regarded as a Heusler alloy with a composition of Fe2FeSi. Fe3Si is recently considered as an excellent candidate for spin injection, since some of the Heusler alloys are predicted to be half metals with 100% spin polarization. In this work, the epitaxial film growth was carried out in a multi-chamber MBE system. Streaky RHEED patterns were observed during the MBE growth of Fe3Si on the atomically flat GaAs(100) surface. High-resolution x-ray diffraction measurements were made on our Fe3Si films and gave a narrow rocking curve of about 0.014°. The lattice mismatch between the film and GaAs was determined to be of about -0.2%. Hence, it was feasible to obtain a perfectly lattice matched epitaxial heterostructure for studying effective spin injection. The magnetic properties were measured at 10K and 300K by SQUID magnetometry. The B-H loops at low fields showed fine features that varied with film growth temperature. The appropriate growth procedure was then carried out to minimize the interface reactions. Otherwise, the in-situ XPS spectra showed that the interfacial Fe–Ga–As reactions were reduced by annealing at higher temperatures. MgO was also successfully grown on GaAs (100) substrate. It was obtained using x-ray diffraction measurement that the single crystal MgO was epitaxially grown on GaAs with a 4:3 lattice coincidence. Hence, it was possible for us to study Fe3Si based tunnel spin injector using an epitaxial MgO as a tunneling barrier.